Less than a month before the end of World War I, a huge painting commemorating the war effort was unveiled in central Paris. Its creators wanted to honor the greatest war the world had ever seen with the greatest painting ever made, and they had spent the previous four years working on it with the help of 150 artists.

The result was the world's largest painting at the time, set on a panoramic canvas measuring 402 feet (122 meters) around and 45 feet (13.7 meters) high. It contained over 5,000 life-size portraits of war heroes, royalty and government officials from the Allies of World War I, with France dominating the stage. The painting was so big that a custom building had to be constructed to accommodate it.

The "Panthéon de la Guerre" (meaning "Pantheon of the War") was unveiled, to great fanfare, on Oct. 19, 1918. In the century that followed, it was chopped up, auctioned off, hidden away and even stored outdoors in a crate for a decade before finding its place on the walls of the National World War I Museum and Memorial in Kansas City, Missouri, 4,500 miles away from the start of its unlikely journey.

The "Panthéon de la Guerre" today (click here for full size: cnn.it/2AdegPt)

A blockbuster of the day

Work on the painting had begun, with astonishing foresight, just a few months into the war, in the winter of 1914. The idea came from two French artists with previous experience in panoramas, Pierre Carrier-Belleuse and Auguste François-Marie Gorguet.

Together, they enlisted an array of painters -- particularly elderly ones, as many young ones were on the front line -- and obtained financial and political support, which was essential due to the scale of the project and the materials required. Among the latter were 18,000 square feet of Belgian linen for the canvas, tons of steel armature to support it and enormous amounts of paint, all of which were at a premium in wartime.

The painting was hung in a complete, uninterrupted circle; visitors descended into a tunnel to emerge right in the middle of it. The custom-built, octagonal building that housed it was enviably located in Rue de l'Université, steps from Les Invalides and just a few blocks from the Louvre. It was inaugurated by French President Raymond Poincaré, himself immortalized on the canvas, less than a month before the end of the war -- timing that was "mostly serendipitous," as Levitch puts it.

The original "Panthéon de la Guerre" (click here for full size: cnn.it/2pXV7uR)

Although a circular painting has, technically no center, the main focus of the "Panthéon de la Guerre" was a temple and staircase, representing the French section that spanned about 122 feet. This segment contained most of the 5,000 figures portrayed in the painting, with the rest split between other Allied nations including Britain, Italy, Russia and the United States, each given a space of around 32 feet or less. The background was meant to represent the battlefields of France and Belgium.

The search for figures worthy of appearing in the artwork was painstaking.

"They sifted through the press and read the citations of the day, to see who was killed and find out who was most deserving of being put in this sort of encyclopedia of the French war effort," Levitch said. "They got photographs of people who had been killed and made sketches from those, while others, such as government officials, were sketched in person."

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Touring to America

The "Panthéon de la Guerre" remained in its Paris home for nine years and was seen by three million people. "It was as much for tourists as it was for the French, and seemed particularly popular with American soldiers," Levitch said.

In 1927, as interest started to wane, it was bought by three American businessmen who wanted to send it on a US tour.

"I think they bought it for something like 250,000 dollars, real money for the time, and it had a very high-profile sendoff that I suspect was meant as much for American eyes as it was for the French," Levitch said.

The creators of the painting were opposed to the sale, fearing they would never see it again, although the buyers promised to eventually return it. The sendoff involved ambassadors and bands playing national anthems, in the hope that the "Panthéon de la Guerre" would cement Franco-American relations. A few modifications were made, most notably the inclusion of more women and African-Americans.

Its first stop was New York's Madison Square Garden, where it attracted one million visitors in eight weeks. "They had an appropriately gargantuan opening night with 25,000 people and lots of notables, but it ended up closing two months ahead of schedule, so they were obviously not making as much money as they had hoped," Levtich said.

The painting, just like the war itself, was perceived very differently in the US. France had suffered about 1.7 million deaths in the conflict, whereas the US, which entered the war in 1917, lost around 117,000. Americans had a faint, mostly celebratory memory of the war; the French a rather vivid, bloody one.

"It was not promoted as the solemn painting that it was," Levitch said. "Instead, there were blow horns and even machine guns in Chicago for the 1933 World Fair. It was almost like a carnival attraction, but that's not the spirit of the painting at all. It's really rather quiet for all its grandiosity."

Nearly sold for scrap

The last stop on the painting's US tour was San Francisco in 1940. At that point, the artwork was falling out of fashion and was sent to a storage facility in Baltimore, where it laid abandoned for 12 years in the almost tomb-like, 55-foot crate originally built for it in Paris. Because the painting was too big to keep indoors, it was left outside, and once the owner stopped paying the storage fee -- due to being caught up in World War II in Europe -- it was auctioned off.

The auction took place in July 1952 and included both the painting and the apparatus required to exhibit it, weighing in at a substantial 10 tons. But although the auction records presented it as "an art object of unusual value," few art connoisseurs showed up and the "Panthéon de la Guerre" went for a paltry $3,400 (around $32,000 in today's money) to William H. Haussner, a local restaurateur who was also an art collector and, incidentally, a German World War I veteran.

"He owned a restaurant in Baltimore (that was) very well known for having good art and bad art -- mostly bad art -- on its walls," Levitch said. "He gets word that this was, at one time, an important artwork, and he doesn't want it to go to the scrap metal collectors who were there to get the armature for the painting -- that's who he was competing against in the auction."

Opening the giant crate was such a massive operation -- 22 workers and a 48-foot trailer truck were involved -- that Life magazine sent reporters to document it. But even with a new owner, the future looked bleak for the painting.

"Haussner tried to find a museum that was willing to take it. He got in touch with the Smithsonian. He was willing to donate it but, unsurprisingly, nobody wanted it. Nobody wanted to create a building for it, or repair it. Even the French Consulate said they didn't want it back. It wasn't considered 'high' art," Levitch said.

But there was one person who wanted it: Daniel MacMorris, himself a US World War I veteran who had seen the painting in Paris during the war. He had even gone on to study with Gorguet, one of the two original creators, and was now a professional artist. Awestruck by the Life magazine article, MacMorris started lobbying Haussner to donate the painting to the Liberty Memorial in Kansas City, the nation's largest World War I memorial, where he worked.

A second life

Haussner eventually agreed, giving the "Panthéon de la Guerre" a second life. It needed to be adapted for its new venue, and MacMorris took on the task. "But he knew that he was not going to be able to save the entire painting, that was actually never his intention," Levitch said.

MacMorris had 70 feet of wall space to work with, and, as he wrote in a 1958 letter to the London Daily Telegraph, he wanted to pay homage to Woodrow Wilson and the League of Nations, the precursor to the UN. But his "rearranging," as he called it, is best known for being US-centric -- with few Russian or Eastern European figures making the cut -- and for keeping almost nothing of the original canvas.

"In terms of square footage, he kept only 7 percent of the original, and also made it into a regular painting that's totally flat against the wall," Levitch said. "He ended up repainting a lot of figures and it looks really good. It's impressive work and it only took a couple of years."

The new, Americanized version of the painting -- which now included Harry Truman and Franklin Roosevelt, among others -- was unveiled in Kansas City on Nov. 11, 1959.

"MacMorris centered it on the US," the museum's archivist, Jonathan Casey, said in a phone interview. "He put Woodrow Wilson and all the American political and military leaders in the center, with the Allies on either side -- the whole 'Panthéon' scene with all the French soldiers was just totally removed. You get a whole different sense from it, with America dominating and coming out (looking) most responsible for the victory."

The Liberty Memorial closed down in the 1994 due to safety concerns around its aging structure, but after a successful renovation it opened again in 2006. In 2014 it was recognized as a national memorial and changed its name to National World War I Museum and Memorial. "The renovation really paid off, and it has made the museum incredibly popular and always crowded," Levitch said. "And people are now paying more attention to the Panthéon and its incredible history."

But what happened to the rest of the original painting? A large portion of the original French section now hangs in another hall at the museum, which also keeps dozens of smaller fragments in its archives and exhibits the most significant ones. MacMorris threw away large portions of the canvas, but he also doled out pieces to friends and acquaintances. Some have ended up in flea markets and online, where Levitch purchased one in 2001. "I spotted it on eBay, but it was not advertised as 'Panthéon de la Guerre.' It's a very tiny fragment, about two feet tall and a foot wide," he said.

"I bought it for 99 dollars, which is more than it's probably worth, but to me it was important."